The invention relates generally to digital data storage systems and, more particularly, to disk-based data storage systems.
A disk drive is a data storage device that stores data in concentric tracks on a disk. Data is written to or read from the disk by spinning the disk about a central axis while positioning a transducer near a target track of the disk. During a read operation, data is transferred from the target track to an attached host through the transducer. During a write operation, data is transferred in the opposite direction. In addition, multiple data conversion operations are generally performed in the path between the transducer and the host during read and write operations. When a request to perform a read or write operation is received, a disk drive will often have to perform a seek operation to move the transducer from a current position to the target track indicated in the request before a data transfer can take place. A servo control loop is generally provided for controlling the motion of the transducer during seek and other operations.
During typical disk drive operation, the transducer does not contact the surface of the disk. Instead, the transducer rides along a cushion of air generated by the motion of the disk. The transducer is normally mounted within a slider structure that provides the necessary lift in response to the air currents generated by the disk. The distance between the transducer/slider and the disk surface during disk drive operation is known as the xe2x80x9cfly heightxe2x80x9d of the transducer. Because the transducer is held aloft during disk drive operation, friction and wear problems associated with contact between the transducer and the disk surface are usually avoided. However, situations may arise where the transducer temporarily contacts the surface of the disk during normal operation. For example, distortions on the disk surface known as asperities can produce regions of reduced fly height that sometimes result in contact between the transducer/slider and the disk surface, which in turn causes thermal asperities in the read signal. In addition, some common disk drive operating events are known to cause a reduction in fly height that can result in transducer/disk contact. For example, it is well known that performing a seek operation in a direction that is radially outward with respect to the disk axis of rotation will typically result in a reduction in fly height. Contact between the transducer/slider and the disk surface caused by such mechanisms should be kept to a minimum to prolong disk drive life and to ensure reliable disk drive operation.
Therefore, there is a need for a method and apparatus for reducing the likelihood of contact between the transducer and the disk surface within a disk drive. There is also a need for a method and apparatus that is capable of providing some degree of control over transducer fly height in a disk drive.
The present invention relates to a disk drive that utilizes seek velocity as a means to control the transducer fly height in the disk drive. In a preferred approach, the disk drive uses a maximum seek velocity value during seek operations that varies based on the particular seek operation being performed. The maximum velocity value that is used for a particular seek is preferably chosen based on the competing concerns of seek time and minimum fly height. In a preferred embodiment, the disk drive uses a different maximum radial transducer velocity during an outward directed seek operation than it does for an inward directed seek operation. In this manner, large reductions in fly height during outward directed seeks are avoided with minimal impact on the average seek time of the disk drive.
In one embodiment, a velocity profile generator within a seek controller is used to generate a seek velocity profile for each seek operation. A closed loop feedback arrangement is then used during the seek operation so that the actual transducer velocity follows the seek velocity profile to a relatively high degree of accuracy. The maximum velocity of the seek velocity profile for each seek operation is selected based upon fly height concerns associated with the individual seek operation. At a minimum, this means that a different maximum profile velocity will be used for inward and outward seeks. Thus, the direction of a newly requested seek operation is first determined and then a unique maximum velocity value corresponding to that direction is used to generate the seek velocity profile for the seek operation. In an extension of this technique, unique maximum seek velocity values can also be specified as a function of radial position (e.g., on a zone by zone basis) in addition to the seek direction. These values are preferably stored within a memory in the disk drive and subsequently accessed when a corresponding seek operation is to be performed.
Using the principles of the present invention, the likelihood of transducer/disk contact during seek operations can be reduced significantly, thus improving overall disk drive reliability. In addition, the inventive principles can be used to improve tribology margin in the disk drive without requiring a radical change in the transducer/disk interface (and the expense associated therewith). Furthermore, the inventive principles provide a flexible method for lowering the overall separation between the transducer and the disk without risking contact therebetween during seek operations.